1. Field of the Invention
The present invention relates to a projection apparatus that forms and projects an image by light emitted from a light source, and particularly to an attaching structure for a cover glass to a light source unit.
2. Description of the Related Art
Inside of a projection apparatus such as a projector and a rear projection television, there are provided a light source unit, an image projecting unit and the like. The light source unit is composed of a light source such as a lamp, a division-type case holding the light source, and the like. The image projecting unit is composed of an image forming device such as a DMD (Digital Micromirror Device), optical devices such as color wheel, lens and mirror, and a division-type case holding these devices, and the like. The respective cases are formed of metal so as to tolerate high heat when the light source emits light. When the light emitted from the light source exits through an opening of the case of the light source unit, and enters the case through an opening of the case of the image projecting unit, an image is formed based on the entering light and projected on a screen by the image forming device and the optical devices.
Among the projection apparatuses, there is a projection apparatus in which in order to prevent ultraviolet contained in the light of the light source from deteriorating the above-described devices of the image projecting unit or from exerting a harmful influence on a human body, a cover glass that removes the ultraviolet from the light emitted from the light source while transmitting the light is attached to the opening of the case of the light source unit, as disclosed, for example, in Patent Documents 1; Japanese Utility Model Registration No. 3092509 and Patent Document 2; Japanese Utility Model Registration No. 3104472. As an attaching structure for this cover glass, as disclosed, for example, in Patent Documents 2 described above, openings allowing the light to exit are provided in a cover plate made of sheet metal for covering a front of the light source, which is attached to a frame of a front case, and a holding plate made of sheet metal for holding the cover glass, and both the plates are joined by screws or the like to sandwich and fix the cover glass by edges of both the openings.
Also, among the projection apparatuses, there is a projection apparatus in which in order to prevent devices around a lamp from being damaged when the lamp as a light source is burst, a cover glass for preventing burst pieces of the lamp from scrambling out of a light source unit is attached to an opening of a case of the light source unit, as disclosed in Patent Documents 3, Japanese Patent Application Laid-Open No. 2004-239975, and Patent Document 4, Japanese Patent Application Laid-Open No. 2005-149841, for example. As an attaching structure for this cover glass, as disclosed, for example, in Patent Document 4, Japanese Patent Application Laid-Open No. 2005-149841, an opening allowing the light to exit is provided in an explosion-proof cover made of a metal cylinder or a heat-resisting resin cylinder, which is a part of the case covering a front of the light source, a tapered fitting portion is provided around the opening, a connecting portion to contact the cover glass is provided at an end portion of a rod-shaped electrode of the lamp, and the cover glass is inserted into the fitting portion to fix it with a heat-resisting adhesive or by a spring member and the connecting portion.